The design of an AA area (effective display area) and pixel driving circuit (as shown in FIG. 1) in a display panel usually used nowadays comprises Gate lines (i.e., gate lines), Data lines (i.e., first data lines), sub-pixel units and multiplexing circuits. The Gate lines are used for realizing line-by-line scanning of the sub-pixel units in the AA area, the data lines are used for charging the sub-pixel units in the AA area, and the multiplexing circuits are used for realizing multiplexed output selection of the Data lines in the display panel. The display panel drives rotation of liquid crystals through the potential of the sub-pixel units to realize the different transmittances required for displaying different images on the display panel, so that the real potentials of the sub-pixel units in the display panel is an important index. However, the real potentials of the sub-pixel units in the display panel cannot be measured by the panel designing solutions provided nowadays. Therefore, during the process such as problem analyzing, the real potential of the sub-pixel units cannot be actually measured by the designing solutions. Because there is no structure designed in the designing solutions provided nowadays for measuring the real potential in the sub-pixel units, the real potential of the sub-pixel units, i.e., the real pixel potential, cannot be accurately obtained.